Exclusive: Defender's departure to fierce rivals Manchester United would be
another blow for Arsenal after losing Bacary Sagna to Manchester City

Thomas Vermaelen, the Arsenal captain, has agreed a deal in principle to join Manchester United this summer. United must now try to negotiate a fee with Arsenal after the World Cup finals, but Vermaelen hopes to move to Old Trafford and is preparing to leave the Emirates Stadium.

Vermaelen has one year remaining on his Arsenal contract and the central defender has found himself pushed out of manager Arsène Wenger’s first-choice team by Laurent Koscielny and Per Mertesacker.

Arsenal are prepared to offer Vermaelen a new deal, but are aware that he does not want to spend another season acting as backup. Koscielny and Mertesacker have signed long-term contracts with the Gunners in the past three months.

Louis van Gaal, the new manager at Old Trafford, is desperate to strengthen United’s defence and believes Vermaelen can find his best form under him. Nemanja Vidic left United to join Inter Milan on a free transfer at the end of the season and the out-of-contract Rio Ferdinand was told he can look for a new club.

Vermaelen has been at Arsenal for five years after signing from the Dutch club Ajax. The defender, 28, got off to a superb start with Arsenal, but injuries curtailed his progress.

Vermaelen earns around £70,000 a week and it is understood that he has verbally agreed a deal with United that would see pay him around £100,000 a week. Arsenal can expect to receive less than £10 million for him with only a year remaining on his contract.

Vermaelen is with the Belgium squad in Brazil for the World Cup finals, but he wants his future sorted out as quickly as possible once the tournament ends. He shares the same agent as Robin van Persie and that is understood to have been key to United’s interest.

Vermaelen took over as Arsenal captain when Van Persie moved to United in 2012, but Wenger is poised to review who wears the Arsenal armband next season – no matter where the Belgium international is playing.

Arsenal have been preparing for the possible departure of Vermaelen by lining up a number of defensive targets including Cardiff City’s Steven Caulker and Virgil van Dijk, of Celtic.

Although Vermaelen is not a first-team starter for Arsenal any more, his departure to United would be another blow for Wenger after losing Bacary Sagna to Manchester City. Sagna’s departure means Wenger is already looking for a new right-back. He also wants at least one striker and an imposing central midfielder.

Vermaelen and Belgium start their World Cup Group H campaign against Algeria on Tuesday in Belo Horizonte.